Plastic container and method of producing the same

ABSTRACT

In a plastic container manufactured by melting blow molding a heated and molten parison extruded from an extruder, a mouth  3  and/or a specified part of a body  2  has a thicker thickness than the body proper. One or more thick parts of the body  2  are continuously or discontinuously formed over part or all a peripheral, height or helical direction of the body of the container. The container enjoys enhanced rigidity, appearance and functionality even when the thickness of its body is considerably reduced.

TECHNICAL FIELD

[0001] The present invention relates to a plastic container with a thinmouth body that is improved in strength, appearance and functionality bymaking the mouth and a specified portion of the body thicker than thebody proper, and a method for manufacturing the plastic container.

BACKGROUND ART

[0002] Demand for plastic containers such as bottles is expected toincrease in the future. At the same time, many efforts are being made toreduce the thickness of bottles so as to lower their cost and reducevolume at the time of waste disposal.

[0003] Generally, plastic bottles are classified into two kinds bymanufacturing method: direct blown bottles and draw blown bottles. Inthe direct blow method, plastic bottles are manufactured by blow moldinga hot parison in a die immediately after heating, melting and thenextruding the parison through the die head of an extruder (melting blowmolding). In the draw blow method, plastic bottles are manufactured bycooling a parison extruded from an extruder or injected from aninjector, thereafter heating the cooled parison again to a temperaturefor drawing and then blow molding it in a die (stretch blow molding).

[0004] Conventionally, the method where a hot parison is blow moldedjust after extrusion from an extruder has been generally used in view ofthermal economy.

[0005] In order to reduce the thickness of direct blow bottles, it is,taking blow ratio into account, necessary to extrude a parison as thinas possible from a die head.

[0006] In melt blow molding, the space between the core and the shell ina die head (die) is changed to adjust the thickness of the parisonlocally. Japanese Patent Laid-open No. S62(1987)-202713 teaches a methodfor making the adjustment by moving the core upward or downward, whereasJapanese Patent Laid-open No. H5(1993)-104525 teaches a method formaking the adjustment by changing the position of the shell.

[0007] In such a conventional technique of changing the space betweenthe core and shell for adjusting the thickness of the parison, it iseasy to gradually change the thickness in small degrees but it isdifficult to abruptly change in the thickness by a large degree.

[0008] This is because a large taper angle of the core is required forabruptly changing the thickness of the parison in the die head. However,if the taper angle is large, the pressure for extruding the resin andthe discharge amount of the resin cannot be sufficiently controlled. Asa result, the thickness of the parison cannot be precisely adjusted.These methods are therefore not practical.

[0009] The conventional techniques are not capable of reducing thethickness of the body and shoulder while maintaining a specifiedthickness of the mouth. If the body and shoulder are made thinner, themouth is disadvantageously made thinner at the same time. Such a thinmouth may deform at the time of capping, leading to insufficient sealingthat may cause problems such as liquid leakage. Further, reamerfinishing of the diameter and surface of the mouth become difficult.

[0010] By the conventional techniques, it was difficult to make only apart of the body thick, while maintaining a thin bottle thicknessoverall. Thus, there has been a limit to the degree that the thicknessof a bottle can be reduced and still obtain the desired strength. Therehas also been a limit to the degree that a bottle can be imparted withdecorative property and the degree that its direction of collapse duringdisposal can be controlled (the amount of functionality that can beimparted).

[0011] This invention was accomplished in light of the foregoingcircumstances. One object of the invention is therefore to provide aplastic container, such as a bottle, of reduced thickness and enhancedstrength, decorative appearance and functionality obtained by making themouth and/or specified parts of the body thicker; and a method formanufacturing the plastic container.

SUMMARY OF THE INVENTION

[0012] The present invention provides a plastic container manufacturedby melting blow molding a heated and molten parison extruded from anextruder, wherein a mouth of the container has a thickness of 1.0 to 5.0mm, a body of the container has a thickness of 0.1 to 1.5 mm, and thethickness ratio of the mouth to the body is in the range of 3 to 50. Thethickness of the plastic container preferably becomes abruptly thinnerfrom the mouth to the shoulder of the container.

[0013] In the so-configured plastic container, even if the thickness ofthe body is made as thin as possible, the thickness of the mouth can bethick enough not to be deformed. Thus, the container of the presentinvention can solve the problems of imperfect capping and difficultreaming.

[0014] The present invention provides a plastic container manufacturedby melting blow molding a heated and molten parison extruded from anextruder, a specified part of the body of the container having increasedthickness. In this container, only the specified part of the body of thecontainer is thick and the body is thin overall.

[0015] The container wherein only a specified part of the body is thickcan be embodied in various ways. For example, one or a plurality ofthick parts can be continuously or discontinuously formed over part orall of the periphery of the body of the container. One or a plurality ofthick parts can be continuously or discontinuously formed over part orall of the height of the body of the container. One or a plurality ofthick parts can be continuously or discontinuously formed helically overpart or all of the body of the container.

[0016] In the above embodiments, the thickness ratio of the thick partsto the body proper is preferably in the range of 1.5 to 10.0.

[0017] As stated above, by forming one or a plurality of thick partscontinuously or discontinuously over part or all of the body in anydirection, the strength of the body can be enhanced, the body can beimparted with decorative property, and/or the functionality of thecontainer can be improved.

[0018] This invention also directed to a method for manufacturing theplastic containers. Specifically, this invention provides a method formanufacturing a plastic container by melting blow molding a heated andmolten parison extruded from an extruder, wherein resin is added to apart of the parison corresponding to the mouth and/or a specified partof the body of the container in a prescribed amount such that the mouthand/or the specified part of the body becomes thicker than the bodyproper when the container is molded.

[0019] The prescribed amount of the resin is preferably added when theparison is extruded and molded by supplying the resin from a dischargeoutlet provided in the die head of the extruder.

[0020] By the method, a prescribed amount of resin is added to aspecified part of a parison (corresponding to the mouth and/or a thickpart of the body) at the time when the parison is molded.

[0021] According to the method of the present invention, by forming oneor a plurality of thick parts continuously or discontinuously in themouth, and in any direction over part or all of the body, a plasticcontainer can be easily and precisely manufactured to have higherstrength in the mouth and body, a decorative appearance, and/or improvedfunctionality.

[0022] The term “body” is sometimes used herein with regard to aninvention container having a neck and a shoulder to include the neck andthe shoulder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a sectional view of an essential part of a bottleaccording to a first embodiment of the present invention.

[0024]FIG. 2 is a sectional view of an essential part of another bottleaccording to the first embodiment of the present invention.

[0025]FIG. 3 is a diagrammatic sectional view of a parison moldingdevice used in a method of manufacturing a bottle according to the firstembodiment of the present invention.

[0026]FIG. 4 is a diagrammatic sectional view of a parison moldingdevice used in a comparative example.

[0027]FIG. 5 is a front view of a bottle according to a secondembodiment of the present invention.

[0028]FIG. 6 is a front view of another bottle according to the secondembodiment of the present invention.

[0029]FIG. 7 is a front view of another bottle according to the secondembodiment of the present invention.

[0030]FIG. 8 is a front view of another bottle according to the secondembodiment of the present invention.

[0031]FIG. 9 is a front view of another bottle according to the secondembodiment of the present invention.

[0032]FIG. 10 is a front view of another bottle according to the secondembodiment of the present invention.

[0033]FIG. 11 is a front view of another bottle according to the secondembodiment of the present invention.

[0034]FIG. 12 is a front view of another bottle according to the secondembodiment of the present invention.

[0035]FIG. 13 is a front view of another bottle according to the secondembodiment of the present invention.

[0036]FIG. 14 is a sectional view taken along line A-A in FIG. 5.

[0037]FIG. 15 is a sectional view taken along line B-B in FIG. 13.

[0038]FIG. 16 is a diagrammatic sectional view of a parison moldingdevice with a monolayer die head used in a method of manufacturing abottle according to the second embodiment of the present invention.

[0039]FIG. 17 is a sectional view of the die head of FIG. 16 with slitsformed therein taken along line I-I in FIG. 16.

[0040]FIG. 18 is a diagrammatic sectional view of a parison moldingdevice with a multilayer die head used in a method of manufacturing abottle according to the second embodiment of the present invention.

[0041]FIG. 19 is a diagrammatic sectional view of a parison moldingdevice with a rotary die head used in a method of manufacturing a bottleaccording to the second embodiment of the present invention.

[0042]FIG. 20 is a sectional view of the die head of FIG. 19 taken alongline II-II in FIG. 19.

BEST MODE OF CARRYING OUT THE INVENTION

[0043] Embodiments of the plastic container and the method formanufacturing the plastic container according to the present inventionwill be explained.

[0044] [First Embodiment of Plastic Container]

[0045] First, a first embodiment will be explained in which the presentinvention is applied to the mouth of a bottle.

[0046]FIG. 1 is a sectional view of an essential part of the plasticcontainer according to the first embodiment.

[0047] A bottle 1 is manufactured by extruding a heated and moltenparison through the die head of an extruder and blow molding it. Forordinary bottles having a volume of 300 ml to 2000 ml, the thickness W₁of the body 2 is 0.3 to 1.3 mm and the thickness W₂ of the mouth 3 is1.0 to 5.0 mm. The ratio of the thickness W₂ of the mouth 3 to thethickness W₁ of the body 2 is in the range of 3.3 to 17.

[0048] If the volume of the bottle is smaller than the above value, thethickness ratio of the body 2 to the mouth 3 becomes smaller. If thevolume of the bottle is larger than the above value, the thickness ratioof the body 2 to the mouth 3 becomes larger. In this case, the thicknessW₁ of the body 2 can be 0.1 to 1.5 mm and the ratio of the thickness W₂of the mouth 3 to the thickness W₁ of the body 2 can be in the range of3 to 50.

[0049] If the ratio of the thickness W₂ of the mouth 3 to the thicknessW₁ of the body 2 is smaller than 3, the strength of the body is weak,while if the ratio exceeds 50, the thickness of the body is too large.

[0050] The thickness of the shoulder 4 between the mouth 3 and the body2 becomes abruptly thinner from the connection 5 between the mouth 3 andthe shoulder 4. The shoulder 4 can be shaped so that its thicknessbecomes continuously thinner without any step as shown in FIG. 1 orbecomes abruptly thinner with a step 5 a as shown in FIG. 2.

[0051] In this embodiment, while the resin added at the mouth 3 ispreferably the same as that of the bottle body proper, use of adifferent resin is acceptable. The resin(s) used are decided based onthe material properties, use, size and the like of the bottle. Theaddition amount of the resin is also controlled based on the materialproperties, use, size and the like of the bottle.

[0052] [Method for Manufacturing Bottle of First Embodiment]

[0053] Next, a method of manufacturing bottles according to a firstembodiment will be explained.

[0054]FIG. 3 is a diagrammatic view showing a molding device used in themethod of manufacturing bottles.

[0055] The device for molding a parison has a main extruder 10, a diehead 20, a sub-extruder 30, storage units 40 and a switching unit 41.

[0056] The main extruder 10 heats and melts a thermoplastic resin andcontinuously supplies it to the die head 20. In the die head 20, thespace between a shell 21 and a core 22 can be adjusted in accordancewith instructions output by a controller (not shown) based on a parisoncontrol program. The die head 20 extrudes the molten resin extruded fromthe extruder 10 while controlling the thickness of the parts of theparison corresponding to the respective parts of the bottle.

[0057] The parison extruded from the die head 20 is immediately suppliedto an ordinary blow molding device (not shown) to be molded into abottle in an ordinary manner.

[0058] The sub-extruder 30 has storage units 40 for temporarily storingmolten resin and a switching unit 41 for switching between storage andsupply of the resin to intermittently extrude the molten resin. Aprescribed amount of the molten resin extruded from the sub-extruder 30is intermittently supplied via the storage units 40, the switching unit41 and a path 44 communicating the storage units 40 with the die head20.

[0059] The storage units 40 are provided with two accumulators 42, 43,and the switching unit 41 is provided with a switching valve 45. Theswitching valve 45 alternately makes and breaks connection between thetwo accumulators 42, 43 and the sub-extruder 30. Further the valve 45alternately makes and breaks connection between the two accumulators 42,43 and the communicating path 44.

[0060] The switching valve 45 and two accumulators 42, 43 also operateaccording to instructions output by the controller (not shown in FIG. 3)based on the parison control program.

[0061] Specifically the accumulator 42 is charged with a prescribedamount of resin extruded from the sub-extruder 30 via the switchingvalve 45. The program designates that a specified portion of the parison(corresponding to the mouth of the bottle) is to be made thicker. Oncethe specified portion has moved to the outlet of the die head 20, theswitching valve 45 is switched according to instructions from thecontroller, and the accumulator 42 operates to supply the charged moltenresin to the die head 20 via the communicating path 44, thereby addingthe resin to the specified portion of the parison.

[0062] At this time, the switching valve 45 connects the accumulator 42to the communicating path 44 and simultaneously connects the accumulator43 to the sub-extruder 30 to charge the accumulator 43 with resinextruded from the sub-extruder 30, as shown in FIG. 3.

[0063] As mentioned above, the two accumulators 42, 43 are alternatelycharged with molten resin from the sub-extruder 30, and alternatelysupply a prescribed amount of the molten resin to the die head 20.

[0064] The switching valve 45 is operated by a cylinder (not shown). Theaccumulators 42, 43 are operated by cylinders 42 a, 43 a, respectively.

[0065] The sub-extruder 30 is not limited to an extruder whichcontinuously extrudes resin at a constant rate. It may instead be anextruder with a reciprocating screw which intermittently extrudes resinat a constant rate. When such an extruder is used, the reciprocatingmotion of the screw of the sub-extruder 30 is controlled in synchronismwith the movement of the switching valve 45 and the accumulators 42, 43.

[0066] As explained above, a prescribed amount of molten resin suppliedfrom the sub-extruder 30 is added to the specified portion of theparison (corresponding to the mouth of the bottle). The parison isimmediately held by a pair of dies (not shown) and pressurized air isthen blown for melting blow molding to produce a bottle. Even if theparison is subjected to melting blow molding so as to make the body 2and shoulder 4 of the bottle 1 thin, the mouth 3 can be molded to havethe required thickness.

[0067] The resin forming the parison is preferably the same as the resinadded to a mouth, but can be different.

[0068] Although a monolayer die head is used in this embodiment, a diehead for forming multiple layers may be similarly used. In this case, abottle with a thick body as well as a thick mouth is obtained. A plasticcontainer with a thick body and a manufacturing method thereof will beexplained in the second embodiment.

EXAMPLES

[0069] Bottles manufactured by the method of this embodiment will becompared with those manufactured using a conventional die and merelyadjusting the space between the shell and the core.

Invention Example

[0070] Bottles were manufactured under the following conditions by usingthe molding device as shown in FIG. 3. (1) Main Extruder Material: Highdensity polyethylene (melting point 132° C.) Temperature of MoltenResin: 200° C. Discharge Rate: 15 Kg/h (2) Sub-extruder Material: Highdensity polyethylene (melting point 132° C.) Temperature of MoltenResin: 200° C. Discharge Rate: 1 Kg/h (3) Temperature of Die Head: 200°C. (4) Bottle Volume: 1000 ml Body Thickness: 0.5 mm Mouth Thickness:2.2 mm Body Inner Diameter: 115 mm Mouth Inner Diameter: 18 mm ThicknessRatio of Mouth to Body: 4.4

Comparative Example

[0071] Bottles were manufactured under the following conditions usingthe molding device as shown in FIG. 4. In FIG. 4, a blow molding sectionis not shown. (1) Main Extruder Material: High density polyethylene(melting point 132° C.) Temperature of Molten Resin: 200° C. DischargeRate: 15 Kg/h (2) Temperature of Die Head: 200° C. (3) Bottle Volume:1000 ml Body Thickness: 0.5 mm Mouth Thickness: 1.2 mm Body InnerDiameter: 115 mm Mouth Inner Diameter: 18 mm Thickness Ratio of Mouth toBody: 2.4

[0072] In the case where bottles were manufactured by the methodaccording to the embodiment of the present invention, even if the bodywas made considerably thin, the thickness of the mouth could bemaintained at the required thickness. On the contrary, in the case wherebottles were manufactured by the conventional method, if the body wasmade considerably thin, the thickness of the mouth was inevitably thin.Satisfactory capping and reaming could not be performed, resulting indefective products.

[0073] According to the first embodiment of the present invention, thebody can be reduced to the minimum practical thickness while maintaininga large mouth thickness.

[0074] [Second Embodiment of Plastic Container]

[0075] FIGS. 5 to 13 show bottles according a second embodiment obtainedby applying the present inventionto the bottle body.

[0076] In the example shown in FIG. 5, three ring-like thick parts 2 aare circumferentially formed in the upper part of the body 2 of a bottle1. Alternatively, as shown in FIG. 6, the body 2 can be formed withdiscontinuous thick parts 2 b.

[0077] When ring-like thick parts are circumferentially formed in thebody of a bottle as shown in FIGS. 5 and 6, even if the thickness of thebottle is thin, the strength is enhanced in the diameter direction sothat the graspability of the bottle is improved. Further, if pressure isapplied to the body 2 in the axial direction at the time of disposal,the bottle 1 will collapse in the axial direction like bellows. That isto say, the functionality of the bottle can be improved; for example,the volume of the bottle can be decreased and the bottle can be madeeasy to dispose of.

[0078] The thick parts 2 a can be distributed over the entire axiallength of the body or at any given region thereof. The number and widthof the parts 2 a can be properly determined based on the purpose of thebottle. The parts 2 a can be formed to protrude integrally outward fromthe body 2 as shown in FIG. 14 by matching the shape of the die formolding the bottle to the position and width of the parts 2 a.

[0079] In the example shown in FIG. 7, a plurality of stripe-like thickparts 2 c are formed along substantially the entire axial length of thebody. When the bottle 1 is given the shape of a square column, the thickparts 2 c can be arranged on all or any side surface of the body 2. Whenthe bottle 1 is given a cylindrical shape, the thick parts can bearranged on the peripheral surface at regular or irregular intervals.Further, the thick parts 2 d can be arranged discontinuously. In thecase of discontinuous thick parts, their sizes can be varied, as shownin FIG. 8.

[0080] By forming thick parts along the axial direction of a bottlebody, the strength of the bottle is enhanced along the axial direction.This enables them to be stacked after filling. Further, if pressure isapplied to the bottle from its sides at the time of disposal, the bottlewill collapse in the diameter direction to assume a plate-like shape, sothat the volume can be easily decreased.

[0081] In the case where thick part(s) are arranged along the axialdirection, the part(s) can be distributed over all or any part in theaxial direction. The number and width of the parts can be properlydetermined according to the purpose of the bottle.

[0082] In the example shown in FIG. 9, a patch-like thick part 2 e isformed at one or more parts of the body 2. If such a patch-like thickpart 2 e is formed at a handle part of the bottle 1, the thin handlepart can be reinforced to make the bottle easier to hold and thestrength can be enhanced against shock such as at dropping. If thepatch-like thick part is formed at a part corresponding to anin-mold-label, it functions as a reinforcement for preventing breakageat the label edge. If it is formed at a part to be printed, thefunctionality of the bottle, such as the rigidity at the time ofprinting and inkability, is improved.

[0083] Like the above-mentioned thick parts, the patch-like thick parts2 e can be formed in any size. If a colored resin, glossy resin, matresin or pearlized resin is used, a bottle with a distinctive appearancecan be obtained.

[0084] In the example shown in FIG. 10, thick parts 2 f and thick parts2 g of different width are alternately formed in the periphery likerings.

[0085] Since resin is added in sets of two or more rings, resins withvarious kinds or colors can be added to obtain a bottle having improvedappearance in addition to advantages like those of the bottle of FIG. 5.

[0086] In the example shown in FIG. 11, a thick part 2 h is helicallyformed in the body periphery. In the example shown in FIG. 8, the bottle1 is shaped like a square column and a thick parts 2 i are formedobliquely on any or all side surfaces of the bottle 1.

[0087] A bottle formed helically or obliquely with the thick part 2 h or2 i has the sane advantages as those of a bottle reinforced in both theaxial and circumferential directions.

[0088] In the case where one or more thick parts are formed helically orobliquely, the parts can be distributed over all or any part of theperipheral surface of the body, as in the above-mentioned bottles. Thenumber and width of the parts can be properly determined depending onthe purpose of the bottle.

[0089] In the bottles shown in FIGS. 5 to 13 and the above-mentionedother modified bottles, the thick parts 2 a to 2 i are formed in thevarious shapes and therefore also function to decorate the bottles. If acolored resin, glossy resin, mat resin or pearlized resin is used as theresin constituting the thick parts 2 a to 2 i, the decorating functionis enhanced and the appearance of the bottles is effectively improved.

[0090] In the example shown in FIGS. 14 and 15, a thick part 2 i iscircumferentially formed in the body 2 and concave parts 2 k (only oneshown) for finger insertion are formed in the part 2 j at diametricallyopposed portions.

[0091] Even if the overall thickness of the body 2 is thin, theprovision of the parts 2 j, 2 k give the bottle 1 excellent graspabilityso that the user can firmly hold the bottle 1. In addition, the user cansecurely hold the bottle 1 by inserting fingers into the concave parts 2k.

[0092] The bottles of the above examples are manufactured by extruding aheated and molten parison through the die head of an extruder and blowmolding it. For 300 ml to 2000 ml bottles currently in general use, thethickness W₃ of a body 2 is 0.3 to 1.3 mm and the thickness W₄ of thickparts 2 a to 2 j is 0.5 to 2.0 mm. The ratio of the thickness W₄ of thethick parts 2 a to 2 j to the thickness W₃ of the body 2 is in the rangeof 1.5 to 5.0.

[0093] If the volume of the bottle is smaller than the above value, thethickness ratio of the body to the thick parts becomes smaller. If thevolume of a bottle is larger than the above value, the thickness ratioof a body to the thick parts becomes larger. In this case, the thicknessW₃ of the body 2 can be 0.1 to 1.5 mm and the ratio of the thickness W₄of the thick parts 2 a to 2 j to the thickness W₃ of the body 2 can bein the range of 5.0 to 10.0.

[0094] A preferred ratio of the thickness W₄ of the thick parts 2 a to 2j to the thickness W₃ of the body 2 is in the range of 1.5 to 10.0. ifthe ratio of the thickness W₄ to the thickness W₃ is smaller than 1.5,the thickness of the thick parts 2 becomes insufficient so that theadvantages of the invention cannot be satisfactorily obtained, while ifthe ratio is greater than 10, the thick parts become unnecessarilythick.

[0095] In the bottles of this embodiment, the resin added to the thickparts 2 a to 2 j can be the same as or different from that of the bodyproper of the bottle. The resin(s) used are decided based on thematerial properties, use, size and the like of the bottle. The additionamount of the resin is also controlled based on the material properties,use, size and the like of the bottle.

[0096] [Method for Manufacturing Bottle of Second Embodiment]

[0097] Next, a method of manufacturing bottles according to a secondembodiment will be explained.

[0098]FIG. 16 is a diagrammatic view showing a molding device used inthe method of manufacturing bottles. The device for molding a parisonshown in FIG. 16 has a main extruder 10, a die head 20, a sub-extruder30, storage units 40 and a switching unit 41. The structure of partsother than the die head 20 is similar to that of the molding deviceshown in FIG. 3.

[0099] Thus, most of the method of manufacturing bottles according tothe second embodiment is the same as the method of manufacturing bottlesaccording to the first embodiment.

[0100] The die head 20 shown in FIG. 16 is provided under a shell 21with a discharge outlet 23 for adding molten resin.

[0101] A die with concave parts corresponding to the thick parts of thebottle can be used as the die in the blow molding device (not shown). Ifa die without any concave or convex parts on the surface thereof isused, thick parts are formed inward of the inner surface of a bottle.However, if concave parts are formed on the surface of the die incorrespondence to the thick parts, the thick parts are protruded outwardfrom the body and the thickness thereof is defined by the depth of theconcave parts.

[0102] For a die used to mold bottles with concave parts 2 k formedmidway between thick part 2 j as shown in FIGS. 13 and 15, convex partsare formed at the parts corresponding to the concave parts 2 k. Thedepth of the concave parts 2 k can be adjusted by adjusting the heightof the convex parts.

[0103] The sub-extruder 30 intermittently supplies molten resin to theoutlet 23 of the die head 20 via the storage units 40, the switchingunit 41, and a path 44 communicating the storage units 40 with the diehead 20.

[0104] Specifically, a parison control program designates that aspecified portion of the parison (corresponding to a thick part of thebottle) is to be made thicker. Once the specified portion has moved tothe outlet of the die head 20, the switching valve 45 is switchedaccording to instructions from the controller, and the accumulator 42operates to supply charged molten resin to the outlet 23 located at thelower part of the die head 20 via the communicating path 44, therebyadding the resin to the specified portion of the parison.

[0105] As mentioned above, the specified portion of the parison(corresponding to the thick part of the bottle) is added with aprescribed amount of molten resin supplied from the sub-extruder 30. Theparison is immediately held by a pair of dies (not shown), andpressurized air is then blown for melting blow molding to produce abottle. Even if the parison is subjected to melting blow molding so asto make the body of a bottle 1 thin, the specified part can be molded tobe thick.

[0106] Next, die heads 20 used in the method of manufacturing bottleswill be explained.

[0107] The die head used in the method of manufacturing bottles can beeither a monolayer die head as shown in FIG. 16 or a multilayer die headas shown in FIG. 18.

[0108] In the multilayer die head of FIG. 18, two discharge outlets 23a, 23 b for adding resin to the parison are provided in the flowdirection of the parison. Since different sub-extruders can supplyresins to the outlets 23 a, 23 b, respectively, two kinds of resins withdifferent material properties, colors or the like can be added to oneand the same parison.

[0109] Alternatively, the same sub-extruder can supply the same resin tothe nozzles 23 a, 23 b.

[0110] In the monolayer and multilayer die heads, the discharge outlet23 can be open along all the periphery of the core 22 to add resin tothe entire periphery of the parison, or can be only partially open toadd resin front part of the periphery of the core 22 (one or morepositions).

[0111]FIG. 17 is a sectional view of the die head of FIG. 16 taken alongline I-I in FIG. 16. As shown in FIG. 17, the periphery of the outlet 23surrounding the core 22 is closed except at four slits and resin isdischarged only from the four slits 24. Such structure where the slits24 are formed for the discharge of resin at part of the peripherysurrounding the core 22 can be applied to a multilayer die head.

[0112]FIG. 19 shows a rotary die head in which a discharge outlet (slit)for adding resin to the parison can rotate. FIG. 20 is a sectional viewof the die head of FIG. 19 taken along line II-II in FIG. 19. Thedischarge outlet 23 is made of a fixed die part 21 a and a rotary diepart 21 b, and a slit 24 is formed at only one portion of the rotary diepart 21 b as shown in FIG. 20. Alternatively, slits may be formed at aplurality of positions. The slit 24 can rotate around the core 22.

[0113] The relationships between these die heads and the bottle shapeswill now be explained.

[0114] When using a monolayer die head with a discharge outlet 24opening along the entire periphery of the core 22, a ring-likecontinuous thick part can be formed in the periphery of the bottle body.In this case, by adding resin one or more times at regulated intervalsduring the molding of the parison, one or more thick parts 4 can beformed in the direction of the height of the body 2 of the bottle 1.FIG. 5 shows a bottle formed with three ring-like continuous thick parts2 a.

[0115] When using a monolayer die head with slits 24 formed at pluralpositions of the periphery of the core 22 and adding resin for a shortperiod of time, a ring-like discontinuous thick part can be formed inthe periphery of the body 2 of the bottle 1. If resin is added threetimes for short periods of time during the extrusion and molding of theparison, a bottle with three ring-like discontinuous thick parts 2 b canbe formed as shown in FIG. 6.

[0116] When resin is continuously added for a long period of time duringthe molding of the parison, a bottle can be obtained that, as shown inFIG. 7, has a plurality of stripe-like thick parts 2 c formed in thedirection of the height of the body 2.

[0117] When resin is added three times with each succeeding additionbeing made a little longer that the previous one during the extrusionand molding of the parison, discontinuous thick parts 2 d varying sizeare formed in the direction of the height of a body 1 as shown in FIG.8.

[0118] Further if the width of a slit is increased, a patch-like thickpart 2 e can be formed as shown in FIG. 9.

[0119] When a multilayer die head with a discharge outlet 24 openingalong the entire periphery of the core 22 is used, two, or a multiple oftwo, different thick parts 2 f, 2 g, . . . (of various widths,materials, colors or the like) can be formed in the periphery of thebottle body 1. The bottle shown in FIG. 10 can be formed by using amultilayer die head with an upper outlet and a lower outlet of narrowerwidth than that of the upper outlet and adding resin twice during themolding of the parison. As a result, two ring-like continuous thickparts 2 f, 2 g with different widths are formed in the periphery of thebody 2.

[0120] When a rotary die head with slits 24 formed in one or pluralpositions of the periphery of the core 22 is used, the bottle shown inFIGS. 11 or 12 is obtained. In the case where the body 2 is a cylinder,if resin is continuously added from one slit while rotating the die headat a relatively high speed during the molding of the parison, a bottlewith a thick part 2 h helically formed on the cylinder body can beobtained as shown in FIG. 11. In the case where a body 2 is a squarecolumn, if resin is added from four slits while rotating the die head ata low speed during the molding of the parison, a bottle with thick parts2 i formed on each of the four side surfaces can be obtained as shown inFIG. 12.

[0121] The above-mentioned relationships between the die heads and thebottle shapes are just examples. Bottles of various shapes can be formedby changing or combining the shape of the discharge outlet of the diehead (with or without a slit(s)); the number and width of a slit(s), andspace between slits; the number of resin additions and the width andperiod of each addition during the molding of the parison; the numberand width of the discharge outlets in a multilayer die head; the rotaryspeed of a rotary slit; and the like. Bottles of various shapes otherthan those shown in the drawings can be provided.

[0122] In the bottles according to the second embodiment of the presentinvention, since a specified part is thicker than the body proper, whilemaintaining the minimum practical thickness of the body, the strength,appearance and functionality of the container can be improved.

[0123] Resins that can be preferably used as the thermoplastic resin inthe first and second embodiments include olefin resins such as highdensity polyethylene, low density polyethylene and polypropylene. Theseolefin resins can be used in combination with other resins such asethylene-vinyl alcohol copolymers, polyamide resins, cyclic olefinresins and polyester resins.

[0124] The present invention is not limited to the above embodiments.

[0125] For example, the first and second embodiments can besimultaneously applied to one and the same plastic container.

[0126] The means for adding resin to the parison is not limited to theaforesaid combination of sub-extruder, switching unit and storage unit,and any of various other means, such as an injector, can be usedinstead. In the case of using an injector, the injection by the injectoris controlled based on programmed instructions from a controller, likein the above embodiments. Further, an extruder with a reciprocatingscrew may be used. In this extruder, resin is stored when the screw ismoved rearward.

[0127] According to the plastic container and method of manufacturingthe container of the present invention described in the foregoing, aspecified part of the container can independently be made thicker thanthe overall container thickness. Thus, in various plastic containersincluding bottles, isolated portions, such as the mouth, a part of thebody desired liable to be bent or to have a decorative appearance, or apart desired to be collapsed in a certain direction, can be madethicker.

[0128] According to the method of manufacturing a plastic container ofthe present invention, the containers described in the foregoing can beeasily and reliably manufactured.

[0129] Industrial Applicability

[0130] As stated above, the present invention can be applied to themouth or the body of plastic containers. In such containers, the mouthor a specified part of the body can be thickened independently of theremaining portions.

What is claimed is:
 1. A plastic container manufactured by melting blowmolding a heated and molten parison extruded from an extruder, wherein amouth of the container has a thickness of 1.0 to 5.0 mm, a body thereofhas a thickness of 0.1 to 1.5 mm, and a thickness ratio of the mouth tothe body is in a range of 3 to
 50. 2. The plastic container according toclaim 1, wherein the thickness becomes abruptly thinner from the mouthto a shoulder.
 3. A method for manufacturing a plastic containermanufactured by melting blow molding a heated and molten parisonextruded from an extruder, wherein a prescribed amount of resin isintermittently added to a part of the parison corresponding to a mouthof the container such that the mouth is thick when the container ismolded.
 4. A plastic container manufactured by melting blow molding aheated and molten parison extruded from an extruder, wherein a specifiedpart of a body of the container has a thicker thickness than the bodyproper.
 5. A plastic container manufactured by melting blow molding aheated and molten parison extruded from an extruder, wherein a mouth anda specified part of a body of the container have thicker thicknessesthan the body proper.
 6. The plastic container according to claim 4 or5, wherein one or a plurality of thick parts are continuously ordiscontinuously formed over part or all of the periphery of the body ofthe container.
 7. The plastic container according to claim 4 or 5,wherein one or a plurality of thick parts are continuously ordiscontinuously formed over part or all of the height of the body of thecontainer.
 8. The plastic container according to claim 4 or 5, whereinone or a plurality of thick parts are continuously or discontinuouslyformed helically over part or all of the body of the container.
 9. Theplastic container according to any one of claims 4 to 8, wherein athickness ratio of the thick parts to the body is in a range of 1.5 to10.0.
 10. A method for manufacturing the plastic container according toany one of claims 4 to 9 manufactured by melting blow molding a heatedand molten parison extruded from an extruder, wherein a prescribedamount of resin is added to a part of a parison corresponding to aspecified part of the body of the container such that the specified partof the body has a thicker thickness than the body proper when thecontainer is molded.
 11. The method according to claim 10, wherein theprescribed amount of the resin is added when the parison is extruded andmolded by supplying the resin from a discharge outlet provided in a diehead of the extruder.
 12. The method according to claim 3, 10 or 11,wherein the prescribed amount of the resin is added by supplying theresin from a sub-extruder or a sub-injector to a discharge outlet. 13.The method according to claim 3, 10 or 11, wherein a die head with aplurality of discharge outlets spaced in a flow direction of the resinis used as the die head of the extruder.
 14. The method according toclaim 11 or 12, wherein a die head with a discharge outlet rotatableabout a core of the die head is used as the die head of the extruder.15. The method according to any one of claims 10 to 14, wherein a diehead with one or a plurality of slits formed in the discharge outlet isused as the die head of the extruder.
 16. The method according to anyone of claims 10 to 16, wherein a material different from a material ofthe container in kind and/or color is used as resin to be added to theparison.